Devices for opening and closing up-and-over doors are known. One of these comprises a geared motor fitted to the up-and-over door and provided with a transversely extending exit shaft connected by articulated vertical arms to couplings rigid with the uprights of the door frame. Rotation of the geared motor causes the articulated arms to rotate about the corresponding frame couplings, with consequent opening and closure of the up-and-over door.
A drawback of this known device is its difficulty of installation, which requires several operations on the up-and-over door for fitting it with external members such as the supports for the geared motor, the support bushes for the transverse shaft, the articulated arms and the relative couplings on the door frame.
A further drawback is that these members increase the weight of the entire door and therefore require adjustment of the counter-weights or the compensation springs to counterbalance said weight.
A further drawback is that the transverse shaft does not allow a usual inwardly opening small service to be applied to the up-and over door.
A further drawback is that up-and-over doors of different width require transverse shafts of corresponding length, with the evident impossibility of constructing standardized operating devices applicable to any up-and-over door.
To obviate these drawbacks an up-and-over door operating device has been proposed comprising a rail to be fixed to the room ceiling to the up-and-over door and able to guide a trolley connected to the door upper cross-member by an articulated bar. The trolley is driven by a belt or chain extending between two sprockets, one of which is driven, so that rotating the motor in one or the other direction causes the trolley to travel along its guide and hence open and close the up-and-over door.
The drawback of this arrangement is a certain constructional complexity due to the large number of components (articulated bar, trolley, trolley guide, chain, chain tensioner, geared motor) and hence the high cost of the device plus the considerable labor involved in its installation.
A further drawback is that the large number of moving parts, each of which is potentially subject to breakdowns, means that its operation is not particularly reliable.
As an alternative to the endless chain it has also been proposed to move the trolley along the guide by a threaded rod driven by a geared motor and engaging a threaded bush rigid with the trolley. In this manner the number of components and hence the installation complexity are reduced while at the same time increasing their reliability of operation, even if in practice the cost of the device plus its installation is not substantially different.